The present invention relates to a novel working fluid for use in a Rankine cycle, and more particularly to a working fluid containing a mixture of 2,2,3,3-tetrafluoropropanol and water suited for use in a Rankine cycle designed to utilize a heat source of low temperature.
Water is the most general working fluid having been employed in Rankine cycle systems, and a steam engine which is a typical Rankine cycle system has been put to practical use from old times. However, the water working fluid has the defects that the range of its use is limited and equipments, particularly equipments using a heat source of low temperature, become large so that the efficiency is lowered, because the freezing point of water is high and its vapor density is low.
In order to improve the defects of the water working fluid, various organic working fluids have been proposed. However, most of them are combustible or corrosive, and a satisfactory working fluid has not been yet obtained. Japanese Patent Examined Publication No. 28271/1976 discloses a mixture of trifluoroethanol and water employed as a working fluid for a Rankine cycle power system. This working fluid is not combustible and not corrosive, but it cannot form an azeotropic-like composition as in the present invention stated after and has not a sufficiently high critical temperature. Therefore, the trifluoroethanol-water working fluid is still unsatisfactory for the Rankine cycle use, and an excellent working fluid for a Rankine cycle is strongly desired.